Many beverages, in particular wine, are sensitive to the presence of oxygen. Wine bottles are often filled with an inert gas, such as nitrogen, before filling with wine so that the space between the wine and the cork contains virtually no oxygen. The amount of oxygen which may seep through the cork is usually small enough so as not to be a problem.
The greatest problem of oxygen in a wine bottle usually arises after a wine bottle has been opened, some of the wine has been consumed and the remainder has been stored for one or more days. One way to reduce this problem is by injecting nitrogen into the space above the wine and then quickly recorking or otherwise resealing the bottle. This of course is only as effective as the seal provided by the cork and the effectiveness of purging the wine bottle of oxygen. Another scheme for reducing the harmful effects of oxygen in an open bottle of wine places the interior of the wine bottle at a partial vacuum. This of course only removes part of the air, of which about twenty-percent is oxygen, and so does not solve the problem, especially for oxygen sensitive wines, such as many white wines.